+/// Enables simultaneously writing and encrypting a byte stream into a Writer.
+struct ChaChaPolyWriter<'a, W: Writer> {
+ pub chacha: &'a mut ChaCha20Poly1305RFC,
+ pub write: &'a mut W,
+}
+
+impl<'a, W: Writer> Writer for ChaChaPolyWriter<'a, W> {
+ // Encrypt then write bytes from `src` into Self::write.
+ // `ChaCha20Poly1305RFC::finish_and_get_tag` can be called to retrieve the tag after all writes
+ // complete.
+ fn write_all(&mut self, src: &[u8]) -> Result<(), io::Error> {
+ let mut src_idx = 0;
+ while src_idx < src.len() {
+ let mut write_buffer = [0; 8192];
+ let bytes_written = (&mut write_buffer[..]).write(&src[src_idx..]).expect("In-memory writes can't fail");
+ self.chacha.encrypt_in_place(&mut write_buffer[..bytes_written]);
+ self.write.write_all(&write_buffer[..bytes_written])?;
+ src_idx += bytes_written;
+ }
+ Ok(())
+ }
+}
+
+/// Enables the use of the serialization macros for objects that need to be simultaneously encrypted and
+/// serialized. This allows us to avoid an intermediate Vec allocation.
+pub(crate) struct ChaChaPolyWriteAdapter<'a, W: Writeable> {
+ pub rho: [u8; 32],
+ pub writeable: &'a W,
+}
+
+impl<'a, W: Writeable> ChaChaPolyWriteAdapter<'a, W> {
+ #[allow(unused)] // This will be used for onion messages soon
+ pub fn new(rho: [u8; 32], writeable: &'a W) -> ChaChaPolyWriteAdapter<'a, W> {
+ Self { rho, writeable }
+ }
+}
+
+impl<'a, T: Writeable> Writeable for ChaChaPolyWriteAdapter<'a, T> {
+ // Simultaneously write and encrypt Self::writeable.
+ fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+ let mut chacha = ChaCha20Poly1305RFC::new(&self.rho, &[0; 12], &[]);
+ let mut chacha_stream = ChaChaPolyWriter { chacha: &mut chacha, write: w };
+ self.writeable.write(&mut chacha_stream)?;
+ let mut tag = [0 as u8; 16];
+ chacha.finish_and_get_tag(&mut tag);
+ tag.write(w)?;
+
+ Ok(())
+ }
+}
+